Investigations of American foulbrood virulence in South Africa and resistance by African honeybees

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dc.contributor.advisorWossler, Theresaen_ZA
dc.contributor.advisorLe Roux, Johannesen_ZA
dc.contributor.authorHristov, Yordanen_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Botany and Zoology.en_ZA
dc.date.accessioned2021-08-29T19:56:53Z
dc.date.accessioned2022-02-22T10:16:58Z
dc.date.available2023-01-04T03:00:13Z
dc.date.issued2021-12
dc.descriptionThesis (PhD)--Stellenbosch University, 2021. en_ZA
dc.description.abstractENGLISH ABSTRACT: Among all bee diseases American foulbrood (AFB) caused by the bacterium Paenibacillus larvae is considered the most dangerous and economically significant. American foulbrood is highly contagious and deadly, killing bee larvae, as well as honeybee colonies. Clinical signss of AFB were identified in Cape honeybee (Apis mellifera capensis) colonies in the Western Cape, South Africa in 2008. The prevalence and distribution of P. larvae genotypes in South Africa, as well as the virulence of the identified P. larvae field strain to and tolerance of honeybee larvae were investigated in an AFB-exposed and unexposed population. Further the progression and severity of AFB was recorded in full-sized Cape colonies over time and correlated to colony hygienic behaviour. To date, clinical AFB infections are still limited to the Western Cape and are caused by P. larvae ERIC I genotype with only two subtypes identified, namely Ab and ab, which suggest that there is not much genetic diversity of P. larvae strains currently in South Africa. The local AFB strains were found to be highly virulent, both to Cape honeybee larvae and to Cape honeybee colonies, while tolerance of individual larvae was low, for both populations, and no better than the tolerance of European honeybee larvae. Yet the Cape honeybee population is exhibiting resilience, which clearly is not as a consequence of individual larval tolerance. We do show however, that Cape honeybees exhibit good hygienic behaviour and this facilitates the fight against AFB, with those colonies showing good hygienic behaviour exhibiting less severe AFB signs. Further, the only difference in AFB resistance between the two populations was at the colony level. Colonies of a non AFB-exposed population, which were sourced from a small-scale managed beekeeping operation with neglible intervention, suffered less severely from AFB than colonies of a previously AFB- exposed population, which were sourced from a large-scale managed commercial beekeeping operation. This indicates that the intensively used, AFB-exposed honeybee population in the Western Cape had not developed increased AFB resistance or undergone natural selection for enhanced hygienic behaviour, having been exposed to AFB exposure. Rather, the intensively used large-scale commercial population has been exposed to a range of stresses that are known to lower overall resistance of colonies to diseases. Despite the recent reduction of clinical AFB cases in the Western Cape we are cautious in our recommendations going forward. American foulbrood spores are extremely environmentally stable and so we advocate for continual monitoring of colonies since the recent AFB outbreak caused serious damages to the South African honeybee industry and future outbreaks could endanger the South African honeybee industry. Thus, to avoid potential losses associated with AFB, the South Africa government should implement monitoring and eradication programmes.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.af_ZA
dc.description.versionDoctorateen_ZA
dc.embargo.terms2022-12-31
dc.format.extent130 pages : illustrations, mapsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/124215
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshBees -- Disease and pest resistanceen_ZA
dc.subject.lcshBees -- South Africaen_ZA
dc.subject.lcshAmerican foulbrood -- South Africa -- Western Capeen_ZA
dc.subject.lcshHoneybee -- Diseasesen_ZA
dc.subject.lcshPollination by beesen_ZA
dc.subject.lcshColony collapse disorder of honeybeesen_ZA
dc.subject.lcshVirulence (Microbiology) -- Genetic aspectsen_ZA
dc.subject.lcshPaenibacillus larvae -- Pathogenesisen_ZA
dc.subject.nameUCTDen_ZA
dc.titleInvestigations of American foulbrood virulence in South Africa and resistance by African honeybeesen_ZA
dc.typeThesisen_ZA
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Doctoral Degrees (Botany and Zoology)